The Weber test is a screening test for hearing performed with a tuning fork. It can detect unilateral (one-sided) conductive hearing loss (middle ear hearing loss) and unilateral sensorineural hearing loss (inner ear hearing loss). The test is named after Ernst Heinrich Weber (1795–1878). Conductive hearing ability is mediated by the middle ear composed of the ossicles: the malleus, the incus, and the stapes. Sensorineural hearing ability is mediated by the inner ear composed of the cochlea with its internal basilar membrane and attached cochlear nerve (cranial nerve VIII). The outer ear consisting of the pinna, ear canal, and ear drum or tympanic membrane transmits sounds to the middle ear but does not contribute to the conduction or sensorineural hearing ability save for hearing transmissions limited by cerumen impaction (wax collection in the ear canal). The Weber test has had its value as a screening test questioned in the literature.
Weber test performance The Weber and the Rinne test ( RIN-ə) are typically performed together when the results of each combined to determine the location and nature of any hearing losses detected. In the Weber test a vibrating tuning fork (Typically 256 Hz or 512 Hz used for Weber vibration test; 512 Hz used for Rinne hearing test) is placed in the middle of the forehead, above the upper lip under the nose over the teeth, or on top of the head equidistant from the patient's ears on top of thin skin in contact with the bone. The patient is asked to report in which ear the sound is heard louder. A normal Weber test has a patient reporting the sound heard equally in both sides. In an affected patient, if the defective ear hears the Weber tuning fork louder, the finding indicates a conductive hearing loss in the defective ear. Also in the affected patient, if the normal ear hears the tuning fork sound better, there is sensorineural hearing loss on the other (defective) ear. However, this assumes that it is known which ear is defective and which is normal (e.g. by the patient telling the clinician that they cannot hear as well in one ear as in the other), when the testing is being done to characterize the type, conductive or sensorineural, of hearing loss that is occurring. In the case where the patient is unaware or has acclimated to their hearing loss, the clinician has to use the Rinne test in conjunction with the Weber to characterize and localize any deficits. That is, an abnormal Weber test is only able to tell the clinician that there is a conductive loss in the ear which hears better or that there is a sensorineural loss in the ear which does not hear as well. For the Rinne test, a vibrating tuning fork (typically 512 Hz) is placed initially on the mastoid process behind each ear until sound is no longer heard. Then, without re-striking the fork, the fork is then quickly placed just outside the ear with the patient asked to report when the sound caused by the vibration is no longer heard. A normal or positive Rinne test is when sound is still heard when the tuning fork is moved to the air near the ear (air conduction or AC), indicating that AC is equal or greater than bone conduction (or BC). Therefore, AC > BC; which is how it is reported clinically for a normal or positive Rinne result. In conductive hearing loss, bone conduction is better than air or BC > AC, a negative Rinne, if the patient reports that they do not hear the fork once it is moved. The Rinne test is not ideal for distinguishing sensorineural hearing loss, as both sensorineural hearing loss and normal hearing report a positive Rinne test (though the sensorineural patient will have a decreased duration of hearing sound once the fork is moved to air). In a normal patient, the Weber tuning fork sound is heard equally loudly in both ears, with no one ear hearing the sound louder than the other (lateralization). Similarly, a patient with symmetrical hearing loss will hear the Weber tuning fork sound equally well, with diagnostic utility only in asymmetric (one-sided) hearing losses. In a patient with hearing loss, the Weber tuning fork sound is heard louder in one ear (lateralization) than the other. This clinical finding should be confirmed by repeating the procedure and having the patient occlude one ear with a finger; the sound should be heard best in the occluded ear. The results of both tests are noted and compared accordingly below to localize and characterize the nature of any detected hearing losses. Note: the Weber and Rinne are screening tests that are not replacements for formal audiometry hearing tests. Reported test accuracy measurements are very variable for clinical screening, surgical candidacy assessments, and estimation of hearing loss severity.
Detection of air conductive hearing loss A patient with a unilateral conductive hearing loss would hear the tuning fork loudest in the affected ear. This is because the ear with the conductive hearing loss is only receiving input from the bone conduction and no air conduction, and the sound is perceived as louder in that ear. This finding is due to the conduction problem of the middle ear (incus, malleus, stapes, and external auditory meatus) which masks the ambient noise of the room, while the well-functioning inner ear (cochlea with its basilar membrane) picks the sound up via the bones of the skull, causing it to be perceived as a louder sound in the affected ear. Another theory, however, is based on the occlusion effect described by Tonndorf et al, in 1966. Lower frequency sounds (as made by the 256 Hz fork) that are transferred through the bone to the ear canal escape from the canal. If an occlusion is present, the sound cannot escape and appears louder on the ear with the conductive hearing loss. Conductive hearing loss can be mimicked by plugging one ear with a finger and performing the Rinne and Weber tests, which will help clarify the above. Humming a constant note and then plugging one ear is a good way to mimic the findings of the Weber test in conductive hearing loss. The simulation of the Weber test is the basis for the Bing test.
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